Understanding Globex vs. RTH
CME Globex is the electronic platform nearly all futures trade on today, and it runs almost 24 hours a day — from Sunday evening through Friday afternoon, with a short daily maintenance break. "Regular Trading Hours" (RTH) is a narrower window inside that session, historically tied to the old floor-trading pit hours, and it's still where the bulk of daily volume happens because it overlaps with the underlying cash market.
Trading outside RTH — the overnight or "Globex-only" session — tends to be thinner, with wider spreads and more headline-driven moves. Many day traders restrict themselves to RTH specifically because of this liquidity difference, especially on index contracts like ES and NQ.